Method and device for analysing flows

ABSTRACT

A method for analyzing and quantifying flows is proposed, in particular for the three-dimensional determination of flow velocity components or the visualization of flows in fluids or gases, along with a device suitable for this purpose. In this context, using an illuminating device ( 12 ) electromagnetic radiation, in particular, of a predefined color, is generated, using which then a detection space ( 25 ) is scanned in the form of light planes ( 19, 18, 17, 20, 21, 22 ) that are arranged spatially one behind the other, that are at least roughly parallel, and that are generated temporally one after the other. The electromagnetic radiation in the detection space ( 25 ) has the result that electromagnetic waves are generated there by particles characterizing the flow, the waves being detected subsequently using at least one image detector ( 16 ) in the form of two-dimensional, in particular color images. In this detection, the frequency spectrum detected by at least one of the image detectors ( 16 ) or the frequency detected by them and/or the intensity detected by them is changed by an appropriate means ( 28, 27 ) as a function of time.

[0001] The present invention relates to a method and a device for analyzing and quantifying flows, especially for the three-dimensional determination of flow velocity components or the three-dimensional visualization of flows in fluids or gases, according to the species of the independent claims.

BACKGROUND INFORMATION

[0002] In the unpublished application DE 199 63 393.2, a method and a device were proposed for the three-dimensional determination of flow velocities in fluids or gases, electromagnetic waves being detected that at least partially are emitted or scattered from particles that are contained in a detection space and that characterize the flow. For this purpose, in temporal succession, at least two at least approximately parallel light planes, arranged spatially one behind the other, are generated using electromagnetic waves of a different frequency or a different frequency spectrum, the detection space being scanned by the waves. In addition, it was also proposed in that document, to record in a frequency-selective manner or a frequency-band-selective manner two-dimensional, especially color images of the scanned area of the detection space using a detection device. The detection device in that publication, by way of example, is a CCD color camera.

[0003] The objective of the present invention, taking the application DE 199 63 393.2 as a point of departure, was to develop an alternative method and a device that is suitable for carrying out this method.

ADVANTAGES OF THE INVENTION

[0004] In contrast to the related art, the method according to the present invention and the device according to the present invention having the characterizing features of the independent claims has the advantage of a reduced apparatus cost, and one less susceptible to fluctuations, in the area of the illumination device, while at the same time maintaining the advantages of the method that are known from the application DE 199 63 393.2. In particular, the data sets arising in the method according to the present invention are relatively small and therefore can be processed and evaluated easily and clearly. In addition, it is now possible advantageously to dispense with color modulation of the incident light beam or laser beam, for example, using an acousto-optical modulator, by undertaking the color coding of the received two-dimensional images on the receiving side, i.e., in the area of the image detector.

[0005] Finally, the method according to the present invention has the advantage that, in comparison, for example, to methods which use high-speed camera systems, significantly reduced scattered light intensities are sufficient.

[0006] Advantageous refinements of the present invention are yielded from the measures cited in the subclaims.

[0007] Advantageously, there are a multiplicity of possibilities to change, as a function of time, the frequency spectrum in response to scanning the detection space detected by the image detector(s) or the frequency detected by the image detector(s) or the intensity detected by them. In this context, it is especially advantageous if, as the image detector, a CCD camera is used, which, for example, has three sensors (chips) for three different colors, for example, red, green, and blue. By changing the exposure times applicable to the individual sensors in the CCD camera and/or by changing the sensitivity of these individual sensors, the image detected by this CCD camera can be changed as a function of time particularly easily, it being possible to synchronize these changes in a simple manner by scanning the detection space using the light planes that are arranged one behind the other and are generated temporally one after the other. Similarly, it is therefore advantageously possible to install a rotating filter, for example, in front of each of these chips located in the CCD camera, so as to change as a function of time, in a defined and periodic manner, the intensity detected by these chips.

[0008] Furthermore, in place of a CCD color camera it is also advantageously possible to use a black/white camera, which has in its interior, for example, three sensors, whose sensitivity to the intensity of the impinging electromagnetic radiation can be changed, in each case separately, as a function of time, so that the sensors can each have assigned to them a false color, for example, red, green, and blue, and a color image of the detection space can be obtained from the images recorded by the individual sensors as a function of time, using superposition, for example, carried out in a computer.

[0009] In any case, it is advantageously achieved in this manner that the two-dimensional image of the detection space finally registered by the image detector is furnished with color information, which is clearly correlated with the location and time of the generation of a light plane in the detection space and therefore of the y-coordinate of the location of a light-scattering or -emitting particle.

[0010] In addition, it is advantageous if the image detector(s), during the scanning of the detection space, are adjusted continuously or step-by-step in their depth of focus, so that in each case an image is formed of the individual light planes at the location of the image detector at least fairly precisely.

DRAWINGS

[0011] The present invention is discussed in greater detail on the basis of the drawings and in the description below.

[0012]FIG. 1 depicts a flow analysis device,

[0013]FIG. 2 depicts a sensor having a front-positioned rotating filter, in a side view,

[0014]FIG. 3 depicts the sensor having a front-positioned filter according to FIG. 2 in a top view,

[0015]FIG. 4 depicts a time-dependent variation of the spectral sensitivity of three sensors in a CCD camera for the colors red, green, and blue, and

[0016]FIG. 5 depicts a representation of a color pattern sequence using different exposure times of three sensors in a CCD camera for the colors, red, green, and blue.

EXEMPLARY EMBODIMENTS

[0017] The crux of the method according to the present invention is that electromagnetic radiation is first generated by an illuminating device, a detection space being scanned by the radiation at least in areas, electromagnetic waves, which at least partially are emitted or scattered from particles contained in the detection space and which characterize the flow to be analyzed, are detected using at least one image detector.

[0018] In this context, a suitable electromagnetic radiation is, for example, a monochromatic electromagnetic radiation or an electromagnetic radiation having a plurality of frequencies or having a preestablished frequency spectrum, in particular, of a predefined color. The electromagnetic radiation used is preferably located in the visible frequency range, but the exemplary embodiment discussed is not limited to this, because in principle basically any electromagnetic radiation can be used as long as suitable image detectors are available. In particular, IR radiation or UV radiation can also be used for the method according to the present invention.

[0019] The illuminating device thus first generates light planes, that are at least roughly parallel and are arranged spatially and temporally one after the other, that scan or raster-scan the detection space or one area of the detection space. However, in this context, in contrast to the teaching of the application DE 199 63 393.2, which is the point of departure of the aforementioned exemplary embodiment, a color modulation of the light beam or laser beam produced by the illuminating device is dispensed with, and a color coding of the two-dimensional images recorded by the image detector is carried out on the receiving side.

[0020] Therefore, first single-color or monochromatic light planes are generated that are at least roughly parallel, which, spatially and temporally arranged one behind the other, scan or raster-scan a detection space. During this scanning process, an image of the detection space is recorded by one or more image detectors, for example, by a 3-chip-CCD color camera arranged on the end face of the detection space. In this context, in order to be able to determine, in the normal direction, i.e., in the y-direction, the positions and therefore the velocities of the particles characterizing the flow to be investigated color codings are undertaken simultaneously with the scanning as a function of the temporally and spatially changing position of the light planes during the image detection.

[0021] Specifically, this can occur, for example, as a result of the fact that the detection volume to be investigated is recorded using a 3-chip CCD color camera, in which each particle generating a scattered light signal is recorded on each of the three sensors or chips of this camera, which represent the primary colors, red, green, and blue. In conventional 3-chip CCD color cameras, this takes place, for example, as a result of the fact that a frequency-selective or frequency-band-selective filter is arranged in front of each chip. However, alternatively, it is also possible to provide a CCD camera with, for example, three black/white chips (b/w sensor), which record as a function of time only the intensities that impinge on them, and from whose images subsequently a color image is produced, the gray-scale signals of the individual sensors, for example, being assigned to the colors of an RGB monitor (red/green/blue). To this extent, each of these b/w sensors represents a defined color of an RGB image, which subsequently is generated in false colors, for example, in a computer.

[0022] If the sensitivity of the individual sensors or chips in the camera is varied as a function of the position of the light plane, the particles characterizing the flow are represented in a mixed color as a function of the proportions of the intensities of the colors, red, green, and blue, in the summation image of the three images of the individual sensors, -the mixed color being linked in a clear-manner to a concrete light plane, i.e., a defined y-coordinate of the location of the particle.

[0023] In this context, on the one hand, it is possible to understand the sensitivity to be varied as the integral sensitivity of a sensor, i.e., its signal as a function of the intensity of the light impinging on the sensor or of the electromagnetic radiation impinging on the sensor, or, on the other hand, it can be understood as the spectral sensitivity of the sensor for a defined frequency or a defined frequency spectrum of the electromagnetic radiation impinging on the sensor, i.e., its signal as a function of the frequency.

[0024] In the example discussed, the described intensity change of the intensity impinging on the individual sensors is further realized by at least one rotating gray filter, which is positioned in front of at least one of the individual sensors or chips in the CCD camera. As an alternative to rotating gray filters, rotating color filters or rotating polarization filters having a front-positioned polarizer can also be used. Furthermore, there also exists the possibility of an electronic change of the intensities or frequency spectra or frequencies detected by the individual sensors or chips of the CCD camera, so that in this manner in a two-dimensional, in particular color image, recorded by the CCD camera, color codings of the individual scattered light signals arise, which are clearly assigned to a specific light plane.

[0025] Finally, it is also possible to use three different CCD cameras, which are each provided with a suitable device for the time-dependant modulation of the detected intensities or the detected frequency spectrum or the detected frequency. In this case, it is necessary that each of the three cameras detects the same image segment, i.e., records the same area of the detection space, which can be realized, for example, by using a generally known beam splitter for dividing the intensity impinging on the cameras used. In-the event that three CCD cameras are used, which in their interiors each have three sensors (chips), which are sensitive to the primary colors, red, green, and blue, or which represent them, it is then provided, by way of example, as was already described above, that rotating gray filters are installed in front of some of the sensors of the CCD camera.

[0026] Furthermore, it is preferably provided for the exemplary embodiments to be discussed further below that, in response to raster-scanning the detection space by the parallel light planes at the location of the image detector(s), an at least substantially uniformly good depth of focus is always assured. For this purpose, the image detector is preferably equipped in each case with an additional device for the continuous or step-by-step adjustment of the depth of focus as a function of the location of the light plane that is in the process of scanning the detection space.

[0027] Overall, therefore, for realizing a rapid color change or a rapid color coding of the two-dimensional images received by the image detector, on the one hand, it is possible to use rotating color or gray filters or a general filter, which change their transmission as a function of time, and which are installed in front of the image detector(s). On the other hand, in conventional CCD cameras having, for example, three sensors (chips), it is also possible to undertake a high frequency multiple illumination of these individual sensors, varying intensities being generated on the individual sensors through varyingly long exposure times or varyingly long exposure pauses.

[0028] In this way, longer exposure times on one of these sensors lead to a greater image intensity of the individual image of this sensor, which ultimately, due to the differing intensity contributions of the individual images and/or of the individual colors, for example, red, green, and blue, assigned in each case to a sensor, results in a defined-color-coding of the summation image of the three sensors in the CCD camera, i.e., the superposition or addition of the images of the individual sensors. The high-frequency multiple exposure, in this context, can extend into the MHZ range.

[0029] In addition to the aforementioned high-frequency multiple exposure of one or more sensors, it is also possible for the individual sensors conditionally or alternatively to use a time-dependent, in particular electronic modulation of the spectral sensitivity or of the integral sensitivity over the entire detected frequency spectrum.

[0030] In this way, an individual sensor in the CCD camera, in particular within one record of a two-dimensional image, can change its spectral or integral sensitivity such that different intensity contributions of the individual sensors in the CCD camera can be realized as a function of time and therefore of the position of the light planes in the direction of normal within one record. In the summation image, stored by the CCD camera, of the images of the individual sensors, this result in a color coding of the direction of normal, i.e., of the y-coordinate, of the particles characterizing the flow as a function of time or of the location of the light plane generated at this time in the detection space.

[0031] Furthermore, it should be mentioned that the method described a above for color coding can also be used in combination.

[0032]FIG. 1 depicts a flow analyzing device 5, already known in similar form from the application DE 199 63 393.2, having an illumination device 12, which is constituted by a light source 10, in particular, a monochromatic, white, or color laser beam, a downstream collimator 13, a polygon scanner 15, and a galvanometer scanner 14. Using this illuminating device 12, a light beam 11 is first generated, which raster-scans a detection space 25 in the form of same-color light planes 17, 18, 19, 20, 21, 22, generated temporally one-after the other, arranged spatially one after the other, and at least roughly parallel. On one end face 26 of detection space 25, an image detector 16 is arranged in the form of a CCD camera, which in its interior has three sensors 16′. These sensors 16′ are represented in image detector 16, for example, in the form of generally known chips, which are sensitive to the colors red, green, and blue. The two-dimensional image, provided by image detector 16 or stored temporarily, is therefore a summation of the images of sensors 16′ and is therefore, in particular, colored. Alternatively, three sensors 16′ in the CCD camera can also each be b/w sensors (black/white), whose gray-scale signals are then each assigned to one color, so that in this way also a two-dimensional color image arises, for example, by assigning these three b/w sensors to the R-, G- and B-terminals of an RGB color monitor (red/green/blue).

[0033] In image detector 16, an electronic control unit 27 is also integrated, using which the exposure times arising on individual sensors 16′ and/or the sensitivities arising on individual sensors 16′ for the specific frequency ranges of these sensors 16′ can be changed. It is also provided that image detector 16 is connected to an evaluation unit 29, for example, a computer, which stores the two-dimensional color images recorded by image detector 16. An evaluation unit 29 is also provided for evaluating the recorded two-dimensional images of detection space 25 using “particles tracking” algorithms or correlation methods, this evaluation taking place by including the spectral composition of the recorded images. In this manner, using an evaluation unit 29, the location of the particles in the scanned area of three-dimensional detection space 25 as well as their spatial shift as a function of time are determined from the recorded two-dimensional images. Taking into account the time duration between the individual scanning processes of detection space 25, a scanning process being understood as a one-time, complete raster-scanning of detection space 25 using light planes 17, 18, 19, 20, 21, and 22, the local flow velocities of the individual particles characterizing the flow can therefore now be determined. In this context, the x- and z-components of the local flow velocities are generated directly from the spatial shift of this particle in the xz plane, whereas the y-component of the local flow velocities of this particle can be determined from the color information generated in the aforementioned manner or from the color coding undertaken of the recorded images.

[0034] In FIG. 1, it is also provided that image detector 16 is connected to illuminating device 12, in particular, to light source 10, via a correlation unit 30. This correlation unit 30 assures, on the one hand, that the temporal change of the detected frequency spectrum, or of the detected frequency and/or of the detected intensity, takes place in a periodic manner in detector 16, and that at the same time this periodic change is correlated or synchronized with the periodic scanning of detection space 25 by light planes 17, 18, 19, 20, 21, 22. In this context, the scanning period of detection space 25 by light planes 17, 18, 19, 20, 21, 22 is preferably equal to the period of the temporal change of the detected frequency spectrum or of the detected frequency and/or of the detected intensity of image detector 16. In addition, the scanning period can also be a whole-number multiple of this period.

[0035]FIG. 2 explains, by way of example, the manner in which at least one of three sensors 16′, which are integrated in image detector 16, is provided with a rotating gray filter 28. In this context, the rotation of this gray filter 28 is correlated via correlation unit 30 with the scanning of detection space 25, such that the intensity, impinging on sensor 16′ as a function of time, of the electromagnetic waves emitted or scattered from the particles contained in detection space 25 and characterizing the flow can be unambiguously assigned to one defined light planes 17, 18, 19, 20, 21, or 22. Overall, it is achieved as a result of rotating gray filter 28 that the two-dimensional image recorded by image detector 16 during the raster-scanning of detection space 25 is changed in its spectral composition and therefore in its color, in that, on the basis of rotating gray filter 28, the contribution of one of sensors 16′ to the recorded image is modulated by the intensity change registered by the sensor. The recorded two-dimensional image, in this context, is the summation of individual images of sensors 16′ that are integrated in image detector 16. To realize the intensity change in sensors 16′ using rotating gray filter 28, the latter is also configured such that, at a constant intensity of the electromagnetic waves impinging on rotating gray filter 28, the intensity detected by sensor 16′ undergoes a periodic modulation corresponding to the rotation of gray filter 28. In this context, the period of the intensity modulation in sensor 16′ preferably corresponds to one complete rotation of gray filter 28.

[0036] The rotational frequency of gray filter 28, according to FIG. 2, concretely amounts, for example, to 20 kHz and is also, in particular, equal to the scanning frequency of detection space 25 by light planes 17, 18, 19, 20, 21, 22, generated in the manner described. In this context, it should also be observed that the scanning frequency used must also of course be adjusted to the flow velocities to be measured. FIG. 3 depicts FIG. 2 in a top view.

[0037]FIG. 4 describes an alternative method to FIGS. 2 and 3 for the temporal change of the frequency spectrum detected by image detector 16 or of the intensity detected by it. According to FIG. 4, in this context, it is first once again provided that image detector 16 is executed in the form of a CCD camera, in whose interior three sensors 16′ are located, which are sensitive to the colors red, green, and blue, or which represent them as b/w sensors. It is also provided that image detector 16 has an electronic control unit 27, which carries out separately for each sensor 16′ a time-dependent variation of the intensity sensitivity of this sensor 161. This time-dependent variation of the sensitivity of individual sensors 16′ is depicted in FIG. 4 for the colors, red, green, and blue.

[0038] On the basis of this variation, the result in the summation image of the individual images of individual sensors 16′, which is registered by image detector 16 in the form of a two-dimensional color image, is a defined color coding of the particles contained in detection space 25 and characterizing the flow. In this context, the color coding contains the information concerning the location of these particles in the y-direction. In this manner, it is possible especially within one record, i.e., by recording one single two-dimensional color image of the investigated area of detection space 25, to ascertain the motion of a particle both in the xz plane as well as in the y-direction, which is perpendicular to the former.

[0039]FIG. 5 describes a method as an alternative to FIG. 4 for color coding, in contrast to FIG. 4 it being not a modulation of the sensitivity of individual sensors 16′ that is undertaken, but rather a change of the exposure times applicable to individual sensors 16′ or chips. In this context, the exposure times can in a generally known manner be carried out by a phase modulation and/or a pulse-width modulation of the drive of individual sensors 16′ using electronic control unit 27. This phase- or pulse-width modulation is simultaneously synchronized, via correlation unit 30, with the scanning of detection space 25 by light planes 17, 18, 19, 20, 21, 22.

[0040] With respect to further details for evaluating the two-dimensional color images of detection space 25 recorded by image detector 16, reference should be made to the application DE 199 63 393.2. The evaluating methods described there can also be used in the case of the exemplary embodiments discussed above.

[0041] It is also possible to determine the flow velocities of the particles in detection space 25 using the method described in detail in that document.

[0042] In this connection, it should also be emphasized either that a two-dimensional color image is recorded by image detector 16 for each scanning process of detection space 25, the image being correlated then with a two-dimensional image of detection space 25 recorded in particular shortly thereafter, or that alternatively, in a two-dimensional color image of detection space 25, a plurality of probing processes is measured, so that the motion of a particle in detection space 25 is yielded directly, as a pointwise track, of optionally differently colored scattered-light points in this two-dimensional color image.

[0043] Reference should also again be made to the fact that the imaging of the flow space or of the detection space 25, as an alternative to a CCD camera, can also be carried out using a 3-chip special camera, for example, a so-called LLT3 camera. In this case, within this camera three sensors 16′ are used in the form of black/white sensors, which represent the colors, red, green, and blue of an RGB image. In evaluation unit 29, the individual colors, through the superposition of the partial images of sensors 16′, are then reconstructed from the ratio of the intensities of the gray-scale partial images of the individual sensors, and are depicted in false colors. Therefore, a color coding of the finally received images of detection space 25 is possible using an LLT3 camera of this type on the basis of the sensitivity or the exposure times impinging on the individual sensors 16′.

[0044] Detection space 25 in the example discussed has dimensions of 10 cm×10 cm×10 cm. The number of light planes 17, 18, 19, 20, 21, 22, arranged one behind the other, amounts to at least three, but usually there is a multiplicity of, for example, 100 to 200 light planes. In addition, in place of polygon scanner 15 in illuminating device 12, it is also possible to use one or more known cylinder lenses. Polygon scanner 15 preferably rotates in accordance with the measuring task, 20,000 to 60,000 r/min, in particular, 40,000 rotations per minute. The scanning velocity, however, can also in principle be raised into the MHZ range, if appropriate, using further optical components. The size of the particles contained in the detection space is typically in the order of magnitude of 1 μm to 60 μm. 

What is claimed is:
 1. A method for analyzing flows, in particular for the three-dimensional determination of flow velocity components or the three-dimensional visualization of flows in fluids or gases, in a detection space (25), at least two at least roughly parallel light planes (19, 18, 17, 20, 21, 22), that are arranged spatially one after the other, being generated temporally one after the other by electromagnetic radiation, in particular, of a predefined color, and being used to scan the detection space (25), at least in regions; and electromagnetic waves, which are at least partially emitted or scattered by particles that are contained in the detection space (25) and that characterize the flow, being detected by at least one image detector (16), wherein, in scanning the detection space (25), a frequency detected by at least one of the image detectors (16) or a frequency spectrum detected by at least one of the image detectors (16) and/or an intensity detected by at least one of the image detectors (16) of the electromagnetic waves emitted or scattered by the particles is changed as a function of time.
 2. The method as recited in claim 1, wherein the spectral composition in images recorded one after the other by at least one of the image detectors (16) and/or the spectral composition within an image, recorded by at least one of the image detectors (16), of at least one area of the detection space (25) is changed as a function of time.
 3. The method as recited in claim 1, wherein the spectral sensitivity of at least one image detector (16), the intensity impinging on at least one of the image detectors (16), and/or the duration of the impingement of the electromagnetic waves on at least one of the image detectors (16), in the scanning of the detection space (25), is changed as a function of time between the images recorded one after the other and/or within one image.
 4. The method as recited in claim 1, wherein the scanning of the detection space (25) is recorded using at least one CCD camera as an image detector (16).
 5. The method as recited in at least one of the preceding claims, wherein a light beam (11), in particular, a color or monochromatic laser beam, is used for generating the at least roughly parallel light planes (19, 18, 17, 20, 21, 22) that are arranged spatially one after the other.
 6. The method as recited in at least one of the preceding claims, wherein the electromagnetic radiation used for generating the light planes (19, 18, 17, 20, 21, 22) is generated in pulse- or continuous wave mode.
 7. The method as recited in at least one of the preceding claims, wherein the parallel light planes (19, 18, 17, 20, 21, 22), generated temporally one after the other and arranged spatially one after the other, scan the detection space (25) such that the image detector (16) detects an illumination of the detection space (25) that is temporally at least roughly continuous.
 8. The method as recited in at least one of the preceding claims, wherein the image detector(s) (16), during the scanning of the detection space (25), are adjusted in their depth of focus continuously or step-by-step, so that the light planes (19, 18, 17, 20, 21, 22), arranged spatially one after the other and generated temporally one after the other, are imaged at the location of the image detector (16) in each case at least fairly sharply.
 9. The method as recited in at least one of the preceding claims, wherein at least two scannings of the detection space (25) take place in a short time interval, in particular, a multiplicity of periodic scannings, a two-dimensional image of the detection space (25) being recorded using the image detector (16), the light emitted or scattered from the particles being measured in at least two scannings of the detection space (25), which, in particular, immediately follow each other.
 10. The method as recited in at least one of the preceding claims, wherein, using the image detector (16), two-dimensional images of the detection space (25) are recorded, the light emitted or scattered from the particles of at least one scanning of the detection space (25) being measured in at least two images, which, in particular, are recorded shortly after each other.
 11. The method as recited in at least one or the preceding claims, wherein the evaluation of the recorded images of the detection space (25) is carried out using “particle tracking” algorithms or correlation methods, taking into account the spectral composition of the recorded images, the location of the particles in the scanned area of the three-dimensional detection space (25) and/or their spatial shift being determined as a function of time from the two-dimensional image(s) recorded.
 12. The method as recited in claim 11, wherein, taking into account the time duration between the scanning processes, the local flow velocities of the individual particles are determined.
 13. The method as recited in at least one of the preceding claims, wherein the temporal change of the detected frequency or of the detected frequency spectrum and/or of the detected intensity occurs periodically.
 14. The method as recited in at least one of the preceding claims, wherein the temporal change of the detected frequency or of the detected frequency spectrum and/or of the detected intensity is correlated or synchronized with the periodic scanning of the detection space (25) in images recorded one after the other by at least one of the image detectors (16) and/or within an image recorded by at least one of the image detectors (16), the scanning period being in particular equal to, or a whole number multiple of, the period of the temporal change of the detected frequency or of the detected frequency spectrum and/or of the detected intensity.
 15. A device for analyzing flows, in particular, for the three-dimensional determination of flow velocity components or for the three-dimensional visualization of flows in fluids or gases, in a detection space (25), it being possible to generate, in temporal succession, using at least one illuminating device (12) at least two-at least roughly parallel light planes (19, 18, 17, 20, 21, 22), which are arranged spatially one behind the other, by electromagnetic radiation having a predefined frequency or predefined frequency spectrum, in particular, of a predefined color, and being used to scan the detection space (25), at least in regions; and electromagnetic waves, which are at least partially emitted or scattered by particles contained in the detection space (25) and which characterize the flow, being detectable by at least one image detector (16), wherein at least one means (27, 28) is provided which, when the detection space (25) is scanned, changes, as a function of time, the frequency detected by the image detector (16) or the frequency spectrum detected by the image detector (16) and/or the intensity detected by the image detector (16), of the electromagnetic waves that are emitted or scattered by the particles.
 16. The device as recited in claim 15, wherein the illuminating device (12) has at least one light source (10), in particular, a laser, a collimator (13), a polygon scanner (15), and a galvanometer scanner (14).
 17. The device as recited in claim 15, wherein the image detector (16) is arranged on at least one end face of the detection space (25), in particular, on an end face (26) of the detection space (25) that is parallel to the generated light planes (17, 18, 19, 20, 21, 22).
 18. The device as recited in claim 15, wherein the image detector (16) is a black/white camera or a color camera, in particular, a CCD camera or a 3-chip camera, which can record two-dimensional color images of at least one area of the detection space (25), or can depict them in false colors.
 19. The device as recited in claim 15 or 18, wherein the camera or the image detector (16) is provided with a device for adjusting the depth of focus.
 20. The device as recited in at least one of claims 15 through 19, wherein the evaluation unit (29), in particular, a computer, is provided for evaluating and/or storing the recorded two-dimensional images.
 21. The device as recited in at least one of claims 15 through 20, wherein a correlation unit (30) is provided for correlating, in particular synchronizing, the temporal change, produced by the means, of the detected frequency spectrum or of the detected frequency and/or the temporal change of the detected intensity on the basis of the scanning of the detection space (25) undertaken by the illuminating device (12).
 22. The device as recited in at least one of claims 15 through 21, wherein the image detector (16) is a CCD camera having three sensors (16′), in particular, three chips, for detecting three different colors or frequency ranges, and the means (27, 28) is an electronic control unit (27) that is integrated, in particular, in the CCD camera, it being possible, using the control unit, to selectively change, as a function of time, the spectral or integral sensitivity of at least one sensor (16′) in the camera and/or the intensity impinging on at least one sensor (16′) in the camera.
 23. The device as recited in at least one of claims 15 through 22, wherein at least three CCD cameras are provided as image detectors (16), which detect an identical area of the detection space (25) and whose detected frequency or detected frequency spectrum and/or whose detected intensity can be changed using an electronic control unit (27), in each case as a function of time.
 24. The device as recited in at least one of claims 15 through 23, wherein the means (27, 28) is a filter, installed at least in front of one image detector (16) or at least in front of one sensor (16′), in particular a chip, of the CCD camera, in particular, a rotating gray filter (28), a rotating color filter, or a rotating polarization filter having an upstream polarizer. 